It seems as though the yellow/purple gates in Ironclaw Munitions Factory don't block enemy attacks (other than interrupting the retrode sneezes), but knights, on the other hand, can't attack enemies through them.
This is especially annoying if a teammate accidentally raises a gate in front of you, blocking all your attacks and allowing the enemy to attack you.
Yeah, them scuttlebots are really good at it although
I've been hit by a many a monster when I thought I
was safe. Now I've learned to stay away from them
walls though so no biggie ;)